The Cell Cycle

Cell Theory All Organisms are composed of one or more cells The cell is the basic unit of organization of organisms All cells come from preexisting cells

Keeping Cells Identical The instructions for making cell parts are encoded in the DNA, so each new cell must get a complete set of the DNA molecules

Two new, identical DNA strands DNA Replication DNA must be copied or replicated before cell division Each new cell will then have an identical copy of the DNA Original DNA strand Two new, identical DNA strands

Identical Daughter Cells Two identical daughter cells Parent Cell

Eukaryotic Chromosomes All eukaryotic cells store genetic information in chromosomes Most eukaryotes have between 10 and 50 chromosomes in their body cells Human body cells have 46 chromosomes or 23 identical pairs

Eukaryotic Chromosomes Each chromosome is composed of a single, tightly coiled DNA molecule Chromosomes can’t be seen when cells aren’t dividing and are called chromatin

Chromosomes in Dividing Cells Duplicated chromosomes are called chromatids & are held together by the centromere Called Sister Chromatids

Interphase Late Interphase Growth stage Cells mature by making more cytoplasm & organelles Cell carries on its normal metabolic activities Late Interphase Synthesis stage DNA is copied or replicated

Two identical copies of DNA Late Interphase Synthesis stage DNA is copied or replicated Two identical copies of DNA Original DNA

What’s Happening? DNA replicates Centrioles, if present replicate Spindle fibers DNA replicates Centrioles, if present replicate Cell prepares for division

Review of Mitosis

Mitosis Division of the nucleus Only occurs in eukaryotes Has four stages Doesn’t occur in some cells such as brain cells Prophase Anaphase Metaphase Telophase

Prophase Chromatin in nucleus condenses to form visible chromosomes Spindle fibers form from the centrioles Chromosomes Nucleolus Cytoplasm Nuclear Membrane

Prophase Nuclear membrane & nucleolus are broken down Chromosomes continue condensing & are clearly visible Spindle fibers attach to the centromere of each chromosome Chromosomes

Prophase What’s Happening? Nuclear membrane disintegrates, nucleolus disappears Chromosomes condense Spindle fibers form

Metaphase Chromosomes, attached to the Spindle fibers, move to the center of the cell Chromosomes are now lined up at the equator

Metaphase Spindle Fibers Chromosomes lined at the Equator

Metaphase What’s Happening? Chromosomes lined up at equator Spindle fibers Chromosomes line up at equator of the cell.

Anaphase Occurs rapidly Sister chromatids are pulled apart to opposite poles of the cell by spindle fibers

Sister Chromatids being separated Anaphase Sister Chromatids being separated

Anaphase What’s Happening? Centromeres divide in two Chromosome Spindle fibers Centromeres divide in two Spindle fibers pull sister chromatids to opposite poles of cell Each pole (future daughter cell) now has an identical set of genes.

Telophase Sister chromatids at opposite poles Spindle disassembles Nuclear envelope forms around each set of sister chromatids Nucleolus reappears

Cytokinesis Means division of the cytoplasm Division of cell into two, identical halves called daughter cells In plant cells, cell plate forms at the equator to divide cell In animal cells, cleavage furrow forms to split cell

Daughter Cells Have the same number of chromosomes as each other and as the parent cell from which they were formed Identical to each other, but smaller than parent cell Must grow in size to become mature cells

Identical Daughter Cells Chromosome number the same, but cells smaller than parent cell

Uncontrolled Mitosis Cancer cells If mitosis is not controlled, unlimited cell division occurs causing cancerous tumors Oncogenes are special proteins that increase the chance that a normal cell develops into a tumor cell Cancer cells

Eukaryotic Cell Division Used for growth and repair Produce two new cells identical to the original cell Cytokinesis Anaphase Prophase Metaphase Telophase

Mitotic Stages

Name each stage as you see it occur? Mitosis Animation Name each stage as you see it occur?

Name the Mitotic Stages: Interphase Prophase Telophase Metaphase Anaphase